A. Javier lopez, Associate Professor of Biological Sciences (untenured), has been at Carnegie Mellon University since September of 1989 and has established a vigorous independent research program. The long term goal of his work is to integrate genetic, molecular, and biochemical methods to understand developmental regulatory mechanisms that function at the level of RNA splicing. This proposal focuses on characterization of the alternative splicing mechanism that regulates the differential expression of distinct mRNAs and protein isoforms encoded by the homeotic gene Ultrabithorax in Drosophila melanogaster. In vitro mutagenesis together with P-element-mediated germline transformation will be used to elucidate the regulatory strategy, focusing on critical tests of a specific model supported by previous results. Similar approaches will be used to characterize the role of sequences within the differentially spliced exons. Genetic interaction screens will be used to identify factors involved in the regulation of splicing. Subsequent genetic, molecular, and biochemical analyses will aim to clone the corresponding genes and to characterize the role of their products. The Department of Biological Sciences provides a supportive, interactive environment for these studies. Dr. Lopez maintains close interactions with faculty members ho study the mechanism of pre-mRNA splicing in yeast, who share an interest in genetic approaches to problems in cellular function, and who study diverse developmental problems in Drosophila and in the sea urchin. A RCDA will play a very important role in enhancing Dr. Lopez's career development. The Department of Biological Sciences will significantly reduce his teaching and committee work, supplement his salary, and provide stipend and tuition support for graduate students in his laboratory. This will enable Dr. Lopez to devote 90% of his time to research, will allow him to seek training in new techniques and experimental approaches, and will substantially increase the resources available to him for this work. Longer term commitments include additional space to accommodate growth in Dr. Lopez's laboratory which is anticipated as a result of the RCDA award.